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Thursday, December 13, 2007

Kenneth Arrow: The Case for Cutting Emissions

Kenneth Arrow argues that cutting greenhouse gas emissions now makes economic sense "even if ... one heavily discounts uncertainty and the future." Thus, "there can be little serious argument about the importance of a policy aimed at avoiding major further increases in carbon dioxide emissions":

The case for cutting emissions, by Kenneth Arrow, Commentary, Project Syndicate: Last fall, the UK issued a major government report on global climate change directed by Sir Nicholas Stern, a top-flight economist. The Stern Review ... argues that huge future costs of global warming can be avoided by incurring relatively modest cost today.

Critics of the report don't think serious action to limit carbon dioxide emissions is justified, because there remains substantial uncertainty about the extent of the costs of global climate change, and because these costs will be incurred far in the future.

However, I believe that Stern's fundamental conclusion is justified: We are much better off reducing carbon dioxide emissions substantially than risking the consequences of failing to act, even if, unlike Stern, one heavily discounts uncertainty and the future. ...

Cost-benefit analysis is a principal tool for deciding whether altering it through mitigation policy is warranted. Two aspects of that calculation are critical. First, it has to be assumed that individuals prefer to avoid risk. ...

The second critical aspect is how one treats future outcomes relative to current ones -- an issue that has aroused much attention among philosophers as well as economists. At what rate should future impacts -- particularly losses of future consumption -- be discounted to the present?

The consumption discount rate should account for the possibility that, as consumption grows, the marginal unit of consumption may be considered to have less social value. This is analogous to the idea of diminishing marginal private utility of private consumption, and is relatively uncontroversial, although researchers disagree on its magnitude.

There is greater disagreement about how much to discount the future simply because it is the future, even if future generations are no better off than us. Whereas the Stern Review follows a tradition among British economists and many philosophers against discounting for pure futurity, most economists take pure time preference as obvious.

However, the case for intervention to keep carbon dioxide levels within bounds (say, aiming to stabilize them at about 550 ppm) is sufficiently strong to be insensitive to this dispute. Consider some numbers from the Stern Review concerning the future benefits of preventing greenhouse gas concentrations from exceeding 550 ppm, as well as the costs of accomplishing this. The ... benefit of mitigating greenhouse gas emissions can be represented as the increase in the annual growth rate from today to 2200 from 1.2 percent to 1.3 percent.

As for the cost of stabilization... Let's assume that costs to prevent additional accumulation of carbon dioxide (and equivalents) come to 1 percent of GNP every year forever, and, in accordance with a fair amount of empirical evidence, that the component of the discount rate attributable to the declining marginal utility of consumption is equal to twice the rate of growth of consumption.

A straightforward calculation shows that mitigation is better than business as usual -- that is, the present value of the benefits exceeds the present value of the costs -- for any social rate of time preference less than 8.5 percent. No estimate of the pure rate of time preference, even by those who believe in relatively strong discounting of the future, has ever approached 8.5 percent.

These calculations indicate that, even with higher discounting, the Stern Review estimates of future benefits and costs imply that mitigation makes economic sense. These calculations rely on the report's projected time profiles for benefits and its estimate of annual costs, about which there is much disagreement. Still, I believe there can be little serious argument about the importance of a policy aimed at avoiding major further increases in carbon dioxide emissions.

    Posted by on Thursday, December 13, 2007 at 01:08 AM in Economics, Environment, Policy | Permalink  TrackBack (0)  Comments (44)

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